1. Field of Invention
The invention relates to a method for fabricating semiconductor devices and, more particularly, a method for altering the material properties of a silicide structure using a gas cluster ion beam (GCIB).
2. Description of Related Art
As the integration density of semiconductor devices continues to increase and the critical dimensions associated with such devices continue to decrease, there has been a corresponding increase in interest in identifying materials and processes for producing low resistance materials that maintain or reduce signal delay. Silicide and salicide (self-aligned silicide) materials and processes have been widely used to lower the sheet resistance and contact resistance for the gate conductor and source/drain regions of MOS devices.
A number of metals, including tungsten, tantalum, zirconium, titanium, hafnium, platinum, palladium, vanadium, niobium, cobalt, nickel and various alloys of such metals have been used to form silicide layers on semiconductor devices. Nickel and nickel alloy, such as Ni(Pt), are attractive metals for forming silicides because the annealing process required to form the desired silicide may be conducted at a relatively low temperature, e.g., below about 550 degrees C. (Celsius). Depending on the reaction conditions, nickel can react with silicon to form dinickel monosilicide (Ni2Si), nickel silicide (NiSi), or nickel disilicide (NiSi2), as the silicidation product. Nickel silicide (NiSi), however, provides the lowest sheet resistance of the three nickel silicide phases.
Defectivity and thermal stability issues with NiSi and Ni(Pt)Si can limit the performance, yield and/or reliability of advanced CMOS devices. Many approaches have been used in the past to improve defectivity and thermal stability issues, including pre-amorphization implant (PAI), pre-clean, ion implant of various species, and composition adjustment of deposited metal used to form the silicide. These approaches are generally aimed at modifying the formation kinetics and/or the thermal stability of the NiSi phase relative to the NiSi2 phase that can form defects and cause shorting. With many of these approaches, there are tradeoffs between yield/reliability and resistance/performance.